For the same breakdown voltage (BVDSS) rating and the same die size, the drain-to-source on-resistance (RDS(ON)) of a so-called “superjunction” field effect transistor (also called a “superjunction MOSFET”) will generally be lower than the RDS(ON) of a conventional non-superjunction MOSFET device. For this reason, superjunction MOSFETs are taking a larger and larger share of the overall MOSFET market as compared to the share attributed to conventional trench-type and planar-type MOSFETs.
FIG. 1 (Prior Art) is a simplified cross-sectional diagram of one type of superjunction MOSFET 101. The vertically oriented charge-balancing pillar structures 102 and 103 of P type semiconductor material are formed by depositing an N− type epitaxial semiconductor layer EPI#1 on an N+ type wafer substrate 104. Regions of P type dopants are implanted into the top surface of EPI#1. These regions are represented by the two co-linear dashed horizontal lines at the top of the EPI#1 layer in the illustration. Then another layer of N− type epitaxial semiconductor material EPI#2 is formed over the first layer. Then another set of regions of P type dopants is implanted into the top surface of EPI#2. Then another layer of N− type epitaxial semiconductor material is formed over the second layer, and yet another set of regions of P type dopants is implanted. After many such epitaxial deposition and implant steps, the P type dopants are made to diffuse so that the vertically oriented P type charge balancing columns 102 and 103 are formed. Surface transistor structures are formed at the top of the overall structure to form the finished superjunction MOSFET device 101.
FIG. 2 (Prior Art) is a simplified cross-sectional diagram of another type of superjunction MOSFET 105. In the manufacture of this device, a thicker epitaxial semiconductor layer 106 is formed on an N+ type wafer substrate 107. Deep trenches 108 and 109 are formed down into epitaxial layer 106. The deep trenches are filled with P type silicon and the upper surface of the overall structure is planarized. Surface transistor structures are then formed at the top of the overall structure resulting in the superjunction MOSFET structure 105 illustrated in FIG. 2. The cost of making such superjunction MOSFETs is generally higher than the cost of making a conventional MOSFET device of the same die size, but for a given RDS(ON) requirement a smaller superjunction MOSFET die can be used. The size of the superjunction MOSFET is so much smaller that the superjunction MOSFET is generally considered more cost effective to manufacture and sell as compared to a conventional MOSFET. Superjunction MOSFETs are cost effective to manufacture and work well in their intended environments as confirmed by the growing market share attributable to superjunction MOSFETs.